ghsa-h79v-798m-6jc3
Vulnerability from github
Published
2024-10-21 12:30
Modified
2024-10-24 15:31
Severity ?
5.5 (Medium) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Details

In the Linux kernel, the following vulnerability has been resolved:

ARM: 9410/1: vfp: Use asm volatile in fmrx/fmxr macros

Floating point instructions in userspace can crash some arm kernels built with clang/LLD 17.0.6:

BUG: unsupported FP instruction in kernel mode
FPEXC == 0xc0000780
Internal error: Oops - undefined instruction: 0 [#1] ARM
CPU: 0 PID: 196 Comm: vfp-reproducer Not tainted 6.10.0 #1
Hardware name: BCM2835
PC is at vfp_support_entry+0xc8/0x2cc
LR is at do_undefinstr+0xa8/0x250
pc : [<c0101d50>]    lr : [<c010a80c>]    psr: a0000013
sp : dc8d1f68  ip : 60000013  fp : bedea19c
r10: ec532b17  r9 : 00000010  r8 : 0044766c
r7 : c0000780  r6 : ec532b17  r5 : c1c13800  r4 : dc8d1fb0
r3 : c10072c4  r2 : c0101c88  r1 : ec532b17  r0 : 0044766c
Flags: NzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
Control: 00c5387d  Table: 0251c008  DAC: 00000051
Register r0 information: non-paged memory
Register r1 information: vmalloc memory
Register r2 information: non-slab/vmalloc memory
Register r3 information: non-slab/vmalloc memory
Register r4 information: 2-page vmalloc region
Register r5 information: slab kmalloc-cg-2k
Register r6 information: vmalloc memory
Register r7 information: non-slab/vmalloc memory
Register r8 information: non-paged memory
Register r9 information: zero-size pointer
Register r10 information: vmalloc memory
Register r11 information: non-paged memory
Register r12 information: non-paged memory
Process vfp-reproducer (pid: 196, stack limit = 0x61aaaf8b)
Stack: (0xdc8d1f68 to 0xdc8d2000)
1f60:                   0000081f b6f69300 0000000f c10073f4 c10072c4 dc8d1fb0
1f80: ec532b17 0c532b17 0044766c b6f9ccd8 00000000 c010a80c 00447670 60000010
1fa0: ffffffff c1c13800 00c5387d c0100f10 b6f68af8 00448fc0 00000000 bedea188
1fc0: bedea314 00000001 00448ebc b6f9d000 00447608 b6f9ccd8 00000000 bedea19c
1fe0: bede9198 bedea188 b6e1061c 0044766c 60000010 ffffffff 00000000 00000000
Call trace:
[<c0101d50>] (vfp_support_entry) from [<c010a80c>] (do_undefinstr+0xa8/0x250)
[<c010a80c>] (do_undefinstr) from [<c0100f10>] (__und_usr+0x70/0x80)
Exception stack(0xdc8d1fb0 to 0xdc8d1ff8)
1fa0:                                     b6f68af8 00448fc0 00000000 bedea188
1fc0: bedea314 00000001 00448ebc b6f9d000 00447608 b6f9ccd8 00000000 bedea19c
1fe0: bede9198 bedea188 b6e1061c 0044766c 60000010 ffffffff
Code: 0a000061 e3877202 e594003c e3a09010 (eef16a10)
---[ end trace 0000000000000000 ]---
Kernel panic - not syncing: Fatal exception in interrupt
---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---

This is a minimal userspace reproducer on a Raspberry Pi Zero W:

#include <stdio.h>
#include <math.h>

int main(void)
{
        double v = 1.0;
        printf("%fn", NAN + *(volatile double *)&v);
        return 0;
}

Another way to consistently trigger the oops is:

calvin@raspberry-pi-zero-w ~$ python -c "import json"

The bug reproduces only when the kernel is built with DYNAMIC_DEBUG=n, because the pr_debug() calls act as barriers even when not activated.

This is the output from the same kernel source built with the same compiler and DYNAMIC_DEBUG=y, where the userspace reproducer works as expected:

VFP: bounce: trigger ec532b17 fpexc c0000780
VFP: emulate: INST=0xee377b06 SCR=0x00000000
VFP: bounce: trigger eef1fa10 fpexc c0000780
VFP: emulate: INST=0xeeb40b40 SCR=0x00000000
VFP: raising exceptions 30000000

calvin@raspberry-pi-zero-w ~$ ./vfp-reproducer
nan

Crudely grepping for vmsr/vmrs instructions in the otherwise nearly idential text for vfp_support_entry() makes the problem obvious:

vmlinux.llvm.good [0xc0101cb8] <+48>:  vmrs   r7, fpexc
vmlinux.llvm.good [0xc0101cd8] <+80>:  vmsr   fpexc, r0
vmlinux.llvm.good [0xc0101d20

---truncated---

Show details on source website

To clipboard 

{
  "affected": [],
  "aliases": [
    "CVE-2024-47716"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2024-10-21T12:15:07Z",
    "severity": "MODERATE"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nARM: 9410/1: vfp: Use asm volatile in fmrx/fmxr macros\n\nFloating point instructions in userspace can crash some arm kernels\nbuilt with clang/LLD 17.0.6:\n\n    BUG: unsupported FP instruction in kernel mode\n    FPEXC == 0xc0000780\n    Internal error: Oops - undefined instruction: 0 [#1] ARM\n    CPU: 0 PID: 196 Comm: vfp-reproducer Not tainted 6.10.0 #1\n    Hardware name: BCM2835\n    PC is at vfp_support_entry+0xc8/0x2cc\n    LR is at do_undefinstr+0xa8/0x250\n    pc : [\u003cc0101d50\u003e]    lr : [\u003cc010a80c\u003e]    psr: a0000013\n    sp : dc8d1f68  ip : 60000013  fp : bedea19c\n    r10: ec532b17  r9 : 00000010  r8 : 0044766c\n    r7 : c0000780  r6 : ec532b17  r5 : c1c13800  r4 : dc8d1fb0\n    r3 : c10072c4  r2 : c0101c88  r1 : ec532b17  r0 : 0044766c\n    Flags: NzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none\n    Control: 00c5387d  Table: 0251c008  DAC: 00000051\n    Register r0 information: non-paged memory\n    Register r1 information: vmalloc memory\n    Register r2 information: non-slab/vmalloc memory\n    Register r3 information: non-slab/vmalloc memory\n    Register r4 information: 2-page vmalloc region\n    Register r5 information: slab kmalloc-cg-2k\n    Register r6 information: vmalloc memory\n    Register r7 information: non-slab/vmalloc memory\n    Register r8 information: non-paged memory\n    Register r9 information: zero-size pointer\n    Register r10 information: vmalloc memory\n    Register r11 information: non-paged memory\n    Register r12 information: non-paged memory\n    Process vfp-reproducer (pid: 196, stack limit = 0x61aaaf8b)\n    Stack: (0xdc8d1f68 to 0xdc8d2000)\n    1f60:                   0000081f b6f69300 0000000f c10073f4 c10072c4 dc8d1fb0\n    1f80: ec532b17 0c532b17 0044766c b6f9ccd8 00000000 c010a80c 00447670 60000010\n    1fa0: ffffffff c1c13800 00c5387d c0100f10 b6f68af8 00448fc0 00000000 bedea188\n    1fc0: bedea314 00000001 00448ebc b6f9d000 00447608 b6f9ccd8 00000000 bedea19c\n    1fe0: bede9198 bedea188 b6e1061c 0044766c 60000010 ffffffff 00000000 00000000\n    Call trace:\n    [\u003cc0101d50\u003e] (vfp_support_entry) from [\u003cc010a80c\u003e] (do_undefinstr+0xa8/0x250)\n    [\u003cc010a80c\u003e] (do_undefinstr) from [\u003cc0100f10\u003e] (__und_usr+0x70/0x80)\n    Exception stack(0xdc8d1fb0 to 0xdc8d1ff8)\n    1fa0:                                     b6f68af8 00448fc0 00000000 bedea188\n    1fc0: bedea314 00000001 00448ebc b6f9d000 00447608 b6f9ccd8 00000000 bedea19c\n    1fe0: bede9198 bedea188 b6e1061c 0044766c 60000010 ffffffff\n    Code: 0a000061 e3877202 e594003c e3a09010 (eef16a10)\n    ---[ end trace 0000000000000000 ]---\n    Kernel panic - not syncing: Fatal exception in interrupt\n    ---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---\n\nThis is a minimal userspace reproducer on a Raspberry Pi Zero W:\n\n    #include \u003cstdio.h\u003e\n    #include \u003cmath.h\u003e\n\n    int main(void)\n    {\n            double v = 1.0;\n            printf(\"%fn\", NAN + *(volatile double *)\u0026v);\n            return 0;\n    }\n\nAnother way to consistently trigger the oops is:\n\n    calvin@raspberry-pi-zero-w ~$ python -c \"import json\"\n\nThe bug reproduces only when the kernel is built with DYNAMIC_DEBUG=n,\nbecause the pr_debug() calls act as barriers even when not activated.\n\nThis is the output from the same kernel source built with the same\ncompiler and DYNAMIC_DEBUG=y, where the userspace reproducer works as\nexpected:\n\n    VFP: bounce: trigger ec532b17 fpexc c0000780\n    VFP: emulate: INST=0xee377b06 SCR=0x00000000\n    VFP: bounce: trigger eef1fa10 fpexc c0000780\n    VFP: emulate: INST=0xeeb40b40 SCR=0x00000000\n    VFP: raising exceptions 30000000\n\n    calvin@raspberry-pi-zero-w ~$ ./vfp-reproducer\n    nan\n\nCrudely grepping for vmsr/vmrs instructions in the otherwise nearly\nidential text for vfp_support_entry() makes the problem obvious:\n\n    vmlinux.llvm.good [0xc0101cb8] \u003c+48\u003e:  vmrs   r7, fpexc\n    vmlinux.llvm.good [0xc0101cd8] \u003c+80\u003e:  vmsr   fpexc, r0\n    vmlinux.llvm.good [0xc0101d20\n---truncated---",
  "id": "GHSA-h79v-798m-6jc3",
  "modified": "2024-10-24T15:31:08Z",
  "published": "2024-10-21T12:30:56Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2024-47716"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/39caf610a63786b3b0ef3348ac015edc19827d6a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/89a906dfa8c3b21b3e5360f73c49234ac1eb885b"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/9fc60f2bdd43e758bdf0305c0fc83221419ddb3f"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/cd595d87e5fdd2fc09ea69359aa85e7f12f4b97b"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}


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